One previous automatic door closing device comprises a weight connected to the door by a flexible cord which is arranged over a pulley system. This arrangement has the disadvantage of closing the door in an accelerating manner; the door usually impacts on the door frame at considerable velocity. Air damped and spring assisted piston-type door closers are also known, but have the disadvantages of not providing a uniform closing speed and requiring frequent bleed valve adjustment to compensate for wear. Furthermore, such door closers require high accuracy in manufacture and expensive engineering is needed for heavy duty applications, such as fire doors.
Examples of prior specifications applicable to door closing devices are as follows:
U.S. Pat. No. 4,003,102 (Hawks et al) PA1 U.S. Pat. No. 2,735,675 (Lindsey) PA1 U.S. Pat. No. 4,126,912 (Johnson) PA1 AU,A specification No. 26756/84 (Brayford) PA1 AU,A specification No. 75066/81 (Driscoll) PA1 AU,B specification No. 527354 (Cassidy) PA1 DE,A specification No. 1178739 (Herman) PA1 FR,A specification No. 2263363 (Gretsch Unitas G.M.B.H.)
The present invention is directed towards providing an apparatus for closing doors or the like which is a new and useful alternative to known arrangements. More particularly it would be desirable to provide a device which could be manufacturered cheaply, be extremely reliable, have low maintenance and operate smoothly.